Isotropic etching is non-directional removal of material from a substrate via a chemical process using an etchant. Etchants can include liquids and plasmas. Liquid chemical etchants are typically corrosive, containing acids or bases and other agents to enhance the etchants ability to remove material from a work piece. Such etchants are used, for example, to efficiently remove unwanted material from a work piece. Isotropic etching is particularly useful for removing unwanted metal, for example copper, from semiconductor wafers.
Isotropic etching metal from a work piece typically produces large volumes of waste, on the order of tens of liters per hour, for example, to process semiconductor wafers through a single etch apparatus. This waste, although moderately dilute, can contain many environmental poisons including metal ions, for example copper. Also, feed stocks for creating the liquid etchant are expensive. Handling large volumes of caustic and toxic waste presents a major challenge, for example, in semiconductor processing where large numbers of work pieces are processed daily.